Emulsion, thermoplastic rubber

Adhesive formulations are most frequently prepared from thermoplastic rubber by solution or hot-melt techniques because commercial thermoplastic rubber is available in dry form only, usually as crumb or pellets. However, formulations can be prepared as emulsions or as powders if desired. 

Formulations based on thermoplastic rubbers can be made into emulsions by dispersing solutions or melts into water containing appropriate surface active agents. Normally, any organic solvent present would be stripped from the emulsion. High shear devices, such as colloid mills or centrifugal pumps, have been successfully used for the emulsifying step. 

Compounding prior to emulsification enables resin and plasticizers to be distributed in an equilibrium manner between the thermoplastic rubber phases as in the adhesives discussed earlier. If the neat or plasticized thermoplastic rubber is emulsified alone and then mixed with a resin emulsion, the thermoplastic rubber will act only as a binder for the resin in the finished product. 

Adhesive, latex An emulsion of rubber or thermoplastic rubber in water. 

Poly(acrylic acid) is insoluble in its monomer but soluble in water. It does not become thermoplastic when heated. The sodium and ammonium salts have been used as emulsion-thickening agents, in particular for rubber latex. The polymer of methacrylic acid (Figure 15.13 (VI)) is similar in properties. 

Latexes are usually copolymer systems of two or more monomers, and their total solids content, including polymers, emulsifiers, stabilizers etc. is 40-50% by mass. Most commercially available polymer latexes are based on elastomeric and thermoplastic polymers which form continuous polymer films when dried [88]. The major types of latexes include styrene-butadiene rubber (SBR), ethylene vinyl acetate (EVA), polyacrylic ester (PAE) and epoxy resin (EP) which are available both as emulsions and redispersible powders. They are widely used for bridge deck overlays and patching, as adhesives, and integral waterproofers. A brief description of the main types in current use is as follows [87]. 

The diversity of release products and the wide range of release problems make classification difficult. One approach is by product form, with subdivisions such as emulsions, films, powders, reactive or inert sprays, reactive coatings, and so on. Another approach is by application, e g., metal casting, rubber processing, thermoplastic injection molding, and food preparation and packaging. 

RESINS (Acrylonitrile-Butadiene-Styrene). Commonly referred to as ABS resins, these materials are thermoplastic resins which are produced by grafting styrene and acrylonitrile onto a diene-rubber backbone. The usually preferred substrate is polybutadiene because of its low glass-transition temperature (approximately —80°C). Where ABS resin is prepared by suspension or mass polymerization methods, stereospedfic diene rubber made by solution polymerization is the preferred diene. Otherwise, the diene used is a high-gel or cross-linked latex made by a hot emulsion process. 

Core-shell rubber (CSR) particles are prepared by emulsion polymerization, and typically exhibit two or more alternating rubbery and glassy spherical layers (Lovell 1996 Chapter 8). These core-shell particles are widely used in thermoplastics, especially in acrylic materials (Lovell, 1996), and have also been used to modify thermosets, such as epoxies, cyanates, vinyl ester resins, etc. (Becu et al., 1995). 

PVCA is a copolymer of vinyl chloride and vinyl acetate. It is a colorless thermoplastic solid with good resistance to water as well as concentrated acids and alkalis. It is obtainable in the form of granules, solutions, and emulsions. Compounded with plasticizers, it yields a flexible material superior to rubber in aging properties. It is widely used for cable and wire coverings, in chemical plants, and in protective garments. 

Key Q powdered resin compositions R = a(jueous latexes, emulsions, dispersions S- organic lacquer solutions and dispersions T - plastisol and organosol formulations U = natural and synthetic rubber compositions V = hot-melt compositions W = thermoplastic masses X = oleoresinous compositions Y = reading formulations, eg.. epoxy and polyester Z = plastic monomers Dry thickness-... 

The above units are randomly arranged in emulsion copolymers, but in solution the polymers may occur in uniform blocks of varying length. These block copolymers are resilient and rubber-like at room temperature, but are thermoplastic at higher temperatures. SBRs are similar to natural rubber, in that they are susceptible to atmospheric oxidation and ozone cracking when stretched in air. They are swollen and weakened by hydrocarbons and halogenated hydrocarbons. However, their resistance to abrasion and ageing is superior to natural rubber. 

Dilute solutions or emulsions containing 0.5-1% of a silicone fluid are extensively used as a release agent for rubber molding. However, their use has been restricted with thermoplastics because of the tendency of the fluids to cause stress cracking in polymers. 

Synthetic rubber, a dimethylbutadiene, was developed as a substitute for natural rubber in Germany during World War I and saw limited use as an adhesive. In the early 1930s, neoprene rubber (then called Duprene) became available to adhesive manufacturers in the United States, and shortly thereafter in Great Britain. Today, neoprene rubber adhesives are available as both thermoplastic and cross-linking systems in both solvent and emulsion formulations. Neoprene rubber is the major base resin for contact adhesives. A limited amount of neoprene rubber is also used in sealants. 

Produced by a solution polymerization process, this material exhibited an ordered molecular structure with the styrene monomer located at the ends of the butadiene monomer chain. In addition, other monomers such as isoprene, ethylene, butylene, and others, could be added to the polymer chain, which further modified basic properties. These materials possess a continuous rubber phase for resilience and toughness, and a discontinuous plastic phase for solubility and thermoplasticity. A variety of different grades are also available for this type of SBR, with differences in molecular weight, differences in the types of monomers used, differences in structural configuration, and differences in the ratio of endblock to midblock. Both emulsion and solution polymerized grades of SBR are available as solvent-based and water-based adhesives and sealants. Block copolymers are extensively used for hot melt formulations and both water-based and solvent-based pressure sensitive adhesive applications. Today, SBR elastomers are the most popular elastomers used for the manufacture of adhesives and sealants. 

PROPERTIES OF SPECIAL INTEREST Standard emulsion SBR is a general purpose rubber. Most widely used synthetic rubber in the world. Better tire tread-wear and aging properties than natural rubber. Good abrasion resistance and crack initiation resistance. Poor in tack and heat build-up. Physical properties are poor without reinforcing fillers. Solution SBR is a speciality rubber and more expensive than emulsion SBR. Solution SBR with high vinyl and styrene levels is used in high performance tire treads to improve wet traction. Also used as impact modifier in plastics and as thermoplastic elastomers. 

Chem. Desarip. Modified dehydrogenated (disproportionated) rosin CAS 8050-09-7 EINECS/ELINCS 232-475-7 Uses Thermoplastic resin in hot-melt-applied adhesives and coating tor paper and paperboard substrates as tackifier and processing aid tor rubber-based adhesives and molding compds. emulsifier tor emulsion polymerization plasticizer, softener, tackifier tor use in contact with food Features Pale, oxidation-resistant si. retards cure Pro rties USDA Rosin N solid, flakes sol. in alcohols, esters, ketones, min. spirits, and aromatic hydrocarbons dens. 1.058 kg/l R B soften, pt. 73 C flash pt. (COC) 209 C acid no. 154 sapon. no. 159... 

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